Why humans have very big brains

Our brains are larger than those of most other species, and hefty even in relation to our body mass. Is this the result of an 'arms race' triggered by social drivers such as competition? Probably not, according to EU-funded research that points primarily to environmental challenges and provided fresh food for thought on human evolution.

Why humans have very big brains

Our brains are larger than those of most other species, and hefty even in relation to our body mass. Is this the result of an 'arms race' triggered by social drivers such as competition? Probably not, according to EU-funded research that points primarily to environmental challenges and provided fresh food for thought on human evolution.

The EU-funded SocialBrain project used a computer model to shed new light on our species distant past. My ultimate interest was to test the social hypotheses that have been dominant for the past few decades, says Mauricio González-Forero of the University of St Andrews, in the United Kingdom.

These hypotheses posit that the complexities of competing or collaborating with other individuals or groups may have led our forebears to grow these disproportionately large brains, he explains. Much to the researchers surprise, they were not supported by the projects findings, González-Forero reports.

Instead, the ecological aspect  the rigours of surviving in harsh environments  emerged as far more significant. Ecological drivers had been eclipsed by the intricacies of interaction as a possible explanation, González-Forero notes, but the outcomes of SocialBrain weigh in on their side.

The contribution of the social challenges is not to increase brain size, but actually to decrease it, he continues, adding that there is a twist. The projects simulations indicate that some forms of social interaction do increase relative brain size  the share of body weight accounted for by the brain, as opposed to its volume in the absolute, he underlines.

Pushed by environmental pressures

The brain burns a lot of energy, he says. Its an expensive organ. González-Foreros simulations find that, past a certain point, investing in ever-bigger brains is simply too costly, in metabolic terms. In particular, SocialBrain concludes that competition between individuals, a type of interaction often assumed to be a major stimulus, is actually counterproductive.

In fact, between-individual competition can cause brain size to collapse, González-Forero observes. If it becomes too tough, individuals do better by not investing in bigger brains but instead reproducing as soon as possible.

So it appears that without challenges such as blistering summers on the savanna and the frost of successive ice ages, we might not have evolved our big brains and the advances that they eventually came to shape  air-conditioning and central heating, for example.

And yet, ecological challenges alone cannot account for this aspect of our evolution, says González-Forero. Plenty of species survive and thrive in very difficult settings without developing an abundance of little grey cells.

Think culture, not competition

An extra ingredient is needed and by all indications it appears to be culture, in the technical sense of individuals learning from each other. As successive generations pass information and skills on to their offspring, knowledge accumulates in a population, boosting the collective know-how beyond the level its members might individually develop from scratch, González-Forero explains.

This cultural contribution is not covered by the model as it currently stands. So far, we just have the hint that it may be whats driving the process, he adds. But this is something we want to do as a next step. We want to actually model this aspect explicitly.

SocialBrain, which ended in September 2018, was backed by a fellowship grant awarded by the Marie Skłodowska-Curie actions programme. It took González-Forero to St Andrews following a postdoc position in Switzerland, where he had developed the computer model on which the project relied. A paper presenting SocialBrains outcomes was published in the journal Nature.

The fellowship gave me the independence to address the question I was interested in, to devote my time fully to this challenge, and to ultimately find these unexpected results, González-Forero comments. SocialBrains exploration of our shared history also appears to have resonated with the media and the public, with substantial coverage dedicated to the research.